854  
FXUS02 KWBC 071602  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1101 AM EST FRI DEC 07 2018  
 
VALID 12Z MON DEC 10 2018 - 12Z FRI DEC 14 2018  
   
..OVERVIEW
 
 
THE PROGRESSIVE YET AMPLIFIED FLOW IS FORECAST TO SLOW DOWN AND  
INCREASE IN AMPLITUDE BY THE END OF NEXT WEEK, POTENTIALLY SETTING  
UP A HEAVY RAIN AND WINTER WEATHER THREAT IN THE EAST. UNTIL THEN,  
THE PATTERN WILL REMAIN QUITE ACTIVE THROUGH THE PACIFIC NORTHWEST  
DOWNSTREAM OF A SWIFT 200KT JET. WITH UPPER RIDGING DEVELOPING  
OVER HUDSON BAY, A DEEP TROUGH OR CLOSED LOW IS LIKELY TO ITS  
SOUTH THROUGH THE LOWER/MID-MISSISSIPPI VALLEY BY THE END OF THE  
WEEK.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
AS THE COMPLEX EASTERN SYSTEM FINALLY EXITS STAGE RIGHT EARLY NEXT  
WEEK (LEAD AND SECONDARY SHORTWAVE FOLLOWED BY THE FINAL KICKER ON  
TUESDAY) RIDGING WILL MOVE INTO THE EAST AS A WESTERN TROUGH DIGS  
THROUGH THE INTERIOR. TO START, THE LATEST DETERMINISTIC MODELS  
(00Z/06Z CYCLE) OFFER REASONABLE CLUSTERING WITH THE EVOLUTION AND  
A BLEND OF THE GFS/ECMWF/UKMET/CANADIAN SERVED AS A STARTING  
POINT. BY WEDNESDAY, THE MODELS DIVERGED WITH THE SPEED OF THE  
TROUGH OUT OF THE WEST INTO THE SOUTHERN PLAINS (GFS QUICKER THAN  
THE ECMWF/UKMET BUT CANADIAN SLOWEST AND NOT PREFERRED) AS WELL AS  
THE TRACK/AMPLITUDE OF AN UPSTREAM TROUGH INTO THE PAC NW  
WEDNESDAY. BY THURSDAY, THE 06Z GFS AND 00Z ECMWF WERE CLOSE TO  
THE AGREEABLE ENSEMBLE MEANS (06Z GEFS/00Z ECMWF ENS MEAN) AS THE  
LEAD TROUGH LIFTS TO THE LAKES AND WEAKENS WHILE THE SECONDARY  
TROUGH DIGS/AMPLIFIES TOWARD ARKANSAS NEXT FRIDAY. FOR SEVERAL  
CYCLES THE MODELS HAVE SHOWED A RATHER WOUND-UP SYSTEM DEVELOPING  
WEST OF THE APPALACHIANS BY THE END OF THE WEEK AND LIKELY  
TRACKING TOWARD THE GREAT LAKES WITH DOWNSTREAM RIDGING ALONG THE  
EAST COAST INTO THE NORTHWESTERN ATLANTIC. OPTED TO KEEP A  
MAJORITY DETERMINISTIC WEIGHTING DUE TO GOOD SYNOPTIC CONSISTENCY  
IN THIS LATE-WEEK SYSTEM THOUGH THE DETAILS WILL LIKELY SHIFT  
AROUND AS ENSEMBLE SPREAD EXPANDS QUICKLY NEXT FRIDAY. BACK TO THE  
WEST, THIRD SYSTEM IN FIVE DAYS MAY IMPACT THE REGION.  
 
   
..WEATHER HIGHLIGHTS AND HAZARDS
 
 
IN THE EAST, EXITING SYSTEM WILL SLIDE ACROSS THE ATLANTIC IN  
SEVERAL PIECES, THE FIRST OF WHICH AS A MARITIME GALE HAZARD BEING  
FOLLOWED BY OPC. IN THE WAKE OF THE LOW AND UPPER TROUGH, COOL  
TEMPERATURES AND HIGH PRESSURE WILL DOMINATE THE EAST  
EARLY/MID-WEEK. TEMPERATURES WILL MODERATE BY NEXT THU/FRI AHEAD  
OF THE DEVELOPING SYSTEM OUT OF THE SOUTHERN PLAINS. THE PACIFIC  
NORTHWEST WILL BE QUITE ACTIVE WITH ROUGHLY A SYSTEM EVERY OTHER  
DAY AS THE UPPER FLOW REMAINS POINTED RIGHT ALONG 50N. HIGHER  
TERRAIN OF WESTERN OREGON/WASHINGTON HAVE THE POTENTIAL FOR  
HEAVIEST PRECIPITATION AMOUNTS (RAIN AND MOUNTAIN SNOW) WITH  
LESSER AMOUNTS FARTHER EAST INTO THE NORTH-CENTRAL GREAT  
BASIN/ROCKIES.  
 
BY THU/FRI, INCREASE IN GULF MOISTURE AND DEVELOPING SURFACE LOW  
WILL PRODUCE AND EXPANDING AREA OF PRECIPITATION ALONG/EAST OF THE  
FRONT AND TO THE NORTH/NORTHWEST OF THE LOW WHERE SOME WINTRY  
WEATHER IS POSSIBLE. THE SIGNAL EXISTS FOR A POTENTIALLY MODEST  
AND LOCALLY HEAVY RAIN THREAT LATE FRIDAY INTO NEXT SATURDAY (JUST  
BEYOND THE MEDIUM RANGE PERIOD) AS ATLANTIC MOISTURE FLOWS INTO  
THE SOUTHEAST AND MID-ATLANTIC.  
 
FRACASSO  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
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